Given the complexity of electrical power systems, it is only natural that electrical faults would occur therewithin. For instance, incidents of short circuit at contactors or transmission lines may generate a fault as an abnormal amount of electric current is experienced in the system. Arc flashes or arc faults occur when an electric current travels through an air gap between energized conductors, or from conductors to ground, absent sufficient insulation or isolation to withstand the applied voltage in the electrical system. In an electrical power system providing different phase of voltage, arc fault incidents occur, for example, phase to phase, phase to ground, or phase to phase to ground.
Arc flash hazards result from a rapid energy release from an arc fault. Even though the duration time of an arc event may last only in measurement of milliseconds, an extraordinary amount of incident energy can nevertheless be generated as electrical arcs usually have a high temperature and thus radiate a heat or heated gas or intense light or pressure of waves within a certain distance from the arc. The amount of heat or energy exposed to a worker is a function of the temperature of the heat source of an arc and the distance therefrom. When incident energy is calculated in the unit of calories per cm2, an energy density of 1.2 Cal/cm2 is sufficient to cause second degree burns on exposed human skin.
Given the seriousness and frequency of injuries from exposure to arc flash incidents, the United States the Occupational Safety and Health Administration (OSHA) is enforcing recommendations by the National Electric Code (NEC) and National Fire Protection Association (NFPA) regarding employee safety procedures when work on energized systems is necessary. For example, one of the requirements under the regulations of the OSHA is the designation of a distance of protection boundary that marks where personnel could not enter without wearing appropriate protective gear and clothing such as fire-retardant suit.
The NFPA-70E guidelines promulgate requirements for safe work practices to protect personnel by reducing exposure to major types of electrical hazards such as arc flashes in compliance with OSHA regulations at workplace. Calculation of incident energy of arc flashes are also suggested by the guidelines. For instance, the Institute of Electrical and Electronic Engineers (IEEE) Standard 1584-2002, hereinafter IEEE Standard 1584, utilizes empirical testing data derived formula for calculating the value of arc incident energy and the distance of the protection boundary.
The IEEE Standard 1584, incorporated herein by reference, provides for methods to determine an arc flash hazard boundary distance and an amount of incident energy that is radiated by the arc that a worker is likely to be exposed to upon working or servicing an electrical equipment or upon being present in the vicinity of the arcing incident. The IEEE calculations uses variables with regard to information of enclosure geometry, wire spacing, and fault duty, etc. The Standard sets forth nine procedure steps in determining arc fault incident energy.
Although the IEEE Standard 1584 has been widely used in the industry to addressing arc flash hazards within electrical systems, it is only applicable to ranges of voltages of 208 to 15,000 volts, operating at 50-60-Hz. However, like electrical systems operative at 60-Hz, systems of 400-Hz similarly require electrical equipment to be installed, tested, maintenance serviced or repaired. Likewise, workers and personnel are similarly subject to burns and other personal injuries caused by exposure to arc flashes as they do in 60-Hz electrical systems.
Thus, there is a need for arc flash analysis for electrical systems operating at frequencies other than the 50 to 60-Hz, for example, in the range of 400-Hz, so as to better quantify and determine arc flash hazards in order to protect workers and to promote safer as well as effective workplaces.